Impact grinding



Sept. 12, 1967 T. P. MELOY 3,341,134

IMPACT GRINDING Filed Dec. 16. 1964 @MGMM United States Patent 3,341,134 IMPACT GRINDING Thomas P. Meloy, Milwaukee, Wis., assignor to Allis- Chalmers Manufacturing Company, Milwaukee, Wis.

Filed Dec. 16, 1964, Ser. No. 418,784

6 Claims. (Cl. 241-) This invention relates to the art of comminution and in particular to methods and apparatus for impact breaking of material particles to achieve size reduction.

According to the present invention such as heat hardened balls, similar to those used in rotary grinding mills, are accelerated and directed at a target zone on a striker plate. Material to be reduced in size is delivered to the striker plate in a manner causing this material to flow through the target zone where impact blows will be applied to the material on the striker plate by the accelerated balls for the purpose of breaking the material to smaller sizes. The principal object achieved by such a system is to propel a grinding media with a force that can be controlled, to achieve impact grinding of material having independently controlled depth and residence time in the target zone.

Although such a system achieves an important improvement in size reducing techniques for terrestrial applications, very important advantages are provided for extraterrestrial projects such as are currently planned for the Earths moon.

The eventual establishment of a permanent lunar base appears to be certain. To make the base self-sufficient raw material must be mined, milled and processed. Since a great part of milling is comminution, the development of efiicient, light-weight mills is imperative. This invention is concerned with a light-weight impact grindingmill which will overcome the inherent disadvantage of the lunars 1/6 accelerational field. This low gravitational field on the lunar surface makes rotary comminution mills impractical because it would require slowly rotating mills of huge diameter. This difiiculty is overcome by the present invention because grinding balls are thrown at the material to be broken as it passes over a target zone on a striker plate, the breaking force is thereby independent of gravitational forces for successful operation.

The invention will next be described in greater detail with reference to the drawing showing a schematic diagram of a system according to the present invention.

Referring to the drawing an adjustably angled striker plate assembly 10 is shown as comprising a striker plate 11 having a central portion providing a target zone 11a for both material 12 to be broken and grinding balls 13 for breaking material 12 in a manner that will appear as the description of the invention proceeds.

The striker plate 11 is pivotally supported along a lower edge thereof by a supporting hinge 15. The upper portion of plate 11 may be supported by an assembly 14 including one or more slide arms 16 having a slot 17. A rigid support member 18 is arranged in a fixed position adjacent slide 16. A nut and bolt assembly 19 is provided to clamp slide arm 16 to support member 18 and secure plate 11 in selected positions.

Material supply conveyers 20, 21 are arranged to deliver and drop the material 12 upon the top surface of striker plate 11. These conveyers may be of conventional design and construction. For example, conveyer 21 is shown as having a pair of rollers 22, 23 with an endless material carrying belt 24 looped over both rolls. Sagging of the upper strand of belt 24 spanning rolls 22, 23 may be lessened by arranging a number of smaller rollers 25 beneath the upper strand of belt 24 and midway between rollers 22, 23. One or both of the rolls 22, 23 may be connected to driving means (not shown) to move the belt in the direction indicated by an arrow. Conveyer 20 may be of similar construction to the described conveyer 21.

A ball throwing assembly 30 is provided that is shown as comprising a pair of spaced rolls 31, 32 with an endless belt 33 looped over both rolls. Upper roll 32 may be adjustably supported by an assembly 34 (similar to the assembly 14) to provide for adjusting the slope of assembly 30. One or both of rolls 31, 32 may be connected to driving means (not shown) to move belt 33 in the direction indicated by the arrow. A plurality of generally concave scoops 35 are attached to the outer surface of the looped belt 33 with concave side of the scoops facing in the direction of travel. The assembly 30 is arranged and supported in a position with the portions of belt 33 spanning rolls 31, 32 making an acute angle with a horizontal plane and with the upward slope being toward plate 11. The arrangement of assembly 30 also 10- cates the upper roll 32 at about the same general elevation as the central portion of striker plate 11 to bring the concave side of scoops 35 into a position facing striker plate 11 as scoops 35 complete their upward travel and make a turn around the upper roll 32 to begin traveling downwardly and away from striker plate 11.

A bin 40 is arranged and supported (by means not shown) below and around the lower roll 31 of the assembly 30 with the upper edge 41 of the bin being positioned at least as high as the central axis of the lower roll 31.

A material sizing screen 50 extends from the level of the striker plate hinge 15 downwardly and horizontally away from hinge 15. An imperforate chute 51 is connected to the lower edge of screen 50 and projects into bin 40. A chute 52 is connected to the lower surface of chute 51 and the chute 52 extends therefrom downward and away from chute 51 and beneath screen 50 to receive material dropping through screen 50. Chute 52 may deposit screened material on a conveyer 53 for disposal or delivery as desired.

To prepare for the operation of the described arrangement bin 40 is filled with a supply of grinding balls 13 to a' level higher than the path taken by scoops 35 as the turnabout roller 31 and begin their upward travel. Slide arm 16 is secured by nut and bolt assembly 19 in a position 'relative to support member 18 that provides de sired retention time of material 12 in the target zone 1111 on striker plate 11. That is, the steeper the slope of plate 11 the shorter the retention time and the flatter the slope of plate 11 the longer will be the retention time of material 12 in the target zone 11a. It is desirable that the supporting assembly 34 be adjusted to provide a slope of the ball throwing assembly 30 that will throw balls 13 at striker plate 11 along a line of flight normal to plate 11.

When the operation of the system begins conveyer 20 delivers material 12 to conveyer 21. Conveyer 21 drops the material 12 on striker plate 11 and the material 12 moves into the target zone 11a. While this action is beginning, the assembly 30 begins dipping scoops 35 into bin 40 to pick up balls 13. The scoops 35 carry the balls upwardly as indicated by the arrow and the balls are thrown at the material 12 in target zone 11a where the material can be broken both by the impact of the fall and by the hammering impact blows of balls 13. Broken pieces 'of the material 12 then pass downwardly over sizing screen 50. Pieces small enough to pass through screen 50 are collected on chute 52 for disposal as desired. Oversize material passes downwardly over screen 50 to chute 51 which deposits such material in bin 40 where it is picked up along with balls and thrown at the target zone on plate 11. Thus pieces of the material 12 are reduced in size -by forces greater than gravitational forces and the system is additionally adapted for extraterrestrial projects.

From the foregoing it will 'be understood that the present invention is possessed of unique advantages. However, such modifications and equivalents of the disclosed concepts such as readily occur to those skilled in the art are intended to 'be included within the scope of this invention. A brief review of some of the important features of the present invention and the advantages thereof will serve to emphasize the significance of concepts set forth in the hereinafter appended claims.

It is important that grinding media such as the balls 13 and the material 12 are separately and independently delivered to an elevation at which each is separately and independently directed at the striker plate 11. The rate of particle movement through the target zone 11a on plate 11 is independently controlled, for example by adjusting the slope of striker plate 11. Movement of particles through the target zone could also be controlled by attaching a vibrator to plate 11. Thus, by controlling the delivery of material 12 and the flow of particles through target zone 11a, the distribution, depth and residence time of particles 12 on plate 11 can be closely and independently controlled to achieve optimum residence time to avoid over grinding and power wasted by over grinding. These achievements are further advanced by the independent control over the acceleration applied to grinding media such as balls 13 whereby the speed, impact density and total force directed at material on plate 11 can be controlled to optimize grinding efiiciency.

Since the grinding media 13 is accelerated and directed at material 12 passing through the target zone 11a at nearly right angles to the path of the media, the grinding action is primarily impact grinding with little power lost to friction by one particle of the grinding media glancing off another particle of the grinding media or particles of the material being ground. Furthermore, by screening material immediately after it passes out of the target zone 11a the grinding media '13 and smaller pieces of the material .12 can be immediately separated, and if desired, the screen 50 may be multideck to first screen out grinding media such as the balls 13 and then screen larger pieces of material '12 for recirculation through the system as may be required to achieve the desired particle size, with a very minimum handling of mixed media and ground material which serves no useful purpose.

From the foregoing review of the advantages of the present invention it can be seen that the apparatus and methods that have been described provide new and improved grinding techniques and the disclosure herein is therefore illustrative only and the invention is not limited thereto.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows.

1. In a method of breaking material particles to reduce the size thereof the steps of feeding particles to be broken upon a surf-ace, accelerating other particles at the particles to be broken on the surface, and controlling the feeding of particles to be broken to and across the surface while independently controlling the acceleration of the other particles at the particles to be broken.

2. In a method of breaking material particles to reduce the size thereof the steps of dropping particles to be broken upon a surface, sliding and tumbling the particles to be broken through a target zone on the surface, throwing other particles at the particles to be broken in the target zone on the surface, screening broken particles, collecting pieces larger than a predetermined screened size and said other particles, scooping a portion of said larger pieces and said other pieces from said collection and throwing said portion of said collection at particles to be broken in the target zone on the surface.

3. In an apparatus for breaking material particles to reduce the size thereof, a sloped striker plate, means supported above said plate for feeding particles to be broken upon said plate, means connected to said plate operative to control the residence time of the particles on said plate, and means operable independently of said feeding means and residence time controlling means for accelerating other particles at the particles on said striker plate.

4. In an apparatus according to claim 3, an over-predetermined-size material sizing screen attached to said plate to receive broken pieces moving down the slope from said target zone.

5. In an apparatus according to claim 3, an adjustable assembly supporting said accelerating means adjustable to aim the line of flight of particles directed by said accelerating means to strike said plate approximately perpendicular thereto.

6. In an apparatus for breaking material particles to reduce the size thereof, a striker plate, means supported above said plate for feeding particles to be broken upon said plate, angle adjusting means connected to said plate operative to elevate one end of said plate to a slope causing the material thrown to slide and tumble downwardly through a target zone on said plate at a rate providing a selected residence time of said material in said zone, and means operable independently of said feeding means and said angle adjusting means for accelerating other particles at particles in the target zone on said striker plate.

References Cited UNITED STATES PATENTS 2,332,701 10/1943 Dowsett 24l-170 WILLIAM W. DYER, IR., Primary Examiner.

GERALD A. DOST, Examiner, 

1. IN A METHOD OF BREAKING MATERIAL PARTICLES TO REDUCE THE SIZE THEREOF THE STEPS OF FEEDING PARTICLES TO BE BROKEN UPON A SURFACE, ACCELERATING OTHER PARTICLES AT THE PARTICLES TO BE BROKEN ON THE SURFACE, AND CONTROLLING THE FEEDING OF PARTICLES TO BE BROKEN TO AND ACROSS THE SURFACE WHILE INDEPENDENTLY CONTROLLING THE ACCELERATION OF THE OTHER PARTICLES AT THE PARTICLES TO BE BROKEN. 